The present application relates to laser based detection systems, and finds particular application in conjunction with low and high-density cell detection and discrimination in blood smears, biological assays, and the like, and will be described with particular reference thereto. However, it is to be appreciated the present concepts will also find application in detection and discrimination of other types of low- or high-density features on various substantially planar surfaces and samples.
Laser based detection systems are widely used in many industries, including printing, bio/life and medical sciences, and are implemented in biochip readers, and laser scanning cytometers, among other detection systems.
In order to achieve high resolution in one category of such devices, laser light is guided through objectives similar to those for microscopes. These objectives utilize multiple lens elements to achieve high magnification and often near- or sub-micron resolution. Since both excitation and emission light are guided through these objectives, the heavy weight of the objectives and their small aperture limits the speed at which the laser light can be moved and thus limits the speed of scanning of a sample.
Fiber Array Scanning Technology (FAST) developed by Palo Alto Research Center (PARC) of Palo Alto, Calif. does not utilize a microscope-type objective. Instead FAST employs a rapid spinning galvanometer or mirror for directing laser light and a large-aperture fiber bundle to collect light emission over a relatively large area. The FAST scanning speed is very high, however, its spatial resolution is currently at a laser spot of approximately 8 μm. Concepts of FAST based systems is described, for example, in published U.S. Patent Applications 2004/0071330 (“Imaging Apparatus and Method Employing a Large Linear Aperture”) and 2004/0071332 (“Apparatus and Method for Detecting and Locating Rare Calls”) to Bruce et al. (each hereby incorporated in their entirety by reference).
The implication of the relatively low spatial resolution (i.e., several μm) is the inability of FAST to detect detailed cellular structures or staining characteristics. Therefore, detected matter other than true positive cells, which often have similar intensity and size of true positives, can therefore register as a potential hit. Even after some rudimentary filtering, such as size/intensity scrutiny, an undesirably large number of potential hits still need to be investigated, using time-consuming microscopy investigation. The occurrences of these false positive hits strongly depend on sample preparation methodology where present techniques do not result in sufficient spatial resolution of a detected image event to differentiate between a false positive and a true positive when FAST type system is used.